Electric furnaces



Jan. 24, 1967 A. J. WALKER 3,300,566

ELECTRIC FURNACES Fi led Dec. 6, 1963 5 Sheets-Sheet 1 FIG. I

Jan. 24, 1967 v WALKER 3,300,566

ELECTRIC FURNACES Filed Dec. 6, 1963 a Sheets-Sheet a FIG. 4.

Jan. 24, 1967 A. J. WALKER ELECTRIC FURNACES 5 Sheets-$heet 3 Filed Dec.6,, 1963 Illll V'Al VAVA Unite States Patent 3,30%,566 ELEQTRlC FURNACESAlan John Walker, Chatham, Kent, England, assignor to Spembly LimitedFiled Dec. 6,1963, Ser. No. 328,586 Claims priority, application GreatBritain, Dec. 8, 1962, 46,421/62 13 Claims. (Cl. 1332) This inventionrelates to an electric furnace, and is primarily concerned with themounting of a resistance heating element and its current supplyconnections there- More particularly, the invention relates to a furnacehaving a tubular resistance heating element which is slotted to providean extended path for the passage of heating current there'along, theelement having a plurality of angularly spaced, axially extended arcuateportions which constitute supporting legs for the element.

It has an object of the invention to provide a mounting for the heatingelement which enables the element to be firmly mounted in goodelectrically conducting engagement with the current feeders which supplythe element, and at the same time assures firm engagement between thecurrent feeders and a cooling water jacket.

Accordingly, the invention provides an electric furnace comprising atubular resistance heating element which is constructed to provide alengthy path for the passage of heating current therealong, the elementhaving at one end of plurality of angularly spaced, axially extendedarcuate portions which constitute supporting legs for the element, atubular water jacket, a plurality of current feeders of arc-uate crosssection each arranged longitudinally of the jacket to lie between thejacket and one of the said portions, the current feeders fitting closelyon the one hand against the inner surface of the Water jacket and beingin heat conducting relationship therewith which electrically insulatedtherefrom, and on the other hand against the outer surface of the saidportion, with which it is in electrically conducting relationship, andclamping means for pressing the said portions against the currentfeeders and the current feeders against the jacket in such a manner thatuniform pressure is exerted over the respective contacting surfacesthrough which heat transfer and flow of current occur.

The invention will now be described by way of example with reference tothe accompanying drawings which show the application of the invention toa furnace of the character described in my British patent specificationNo. 908,667.

In the drawings:

FIGURE 1 is a vertical section through the furnace;

FIGURE 2 is a vertical section through the water jacket;

FIGURE 3 is a vertical section of the lower part of the furnace showinga modification;

FIGURE 4 is a sectional plan on the line XX of FIGURE 3;

FIGURE 5 is a vertical section through the furnace when a alternativeheating element is employed.

The furnace includes a tubular water jacket, which comprises arelatively thick inner shell 1 and a thin outer shell 2, has its innershell welded at its upper end in a central aperture in a furnace baseplate 3. The outer shell is constructed to provide a spiral water pathbetween the shells. The outer shell is extended at its upper end in ahorizontal plane to enclose a water path between the extension and theunderside of the base plate in the vicinity of the central aperture. Awater inlet connection 4 is provided at the lower end of the jacket andan outlet connection 5 is provided in the extension. A plate 6 welded tothe lower end of the jacket is provided with apertures 7 through whichthe furnace may be evacuated or supplied with an inert gas. Anadditional connection 8 may be provided to the interior of the ductformed by the jacket which can be fitted with a vacuum gauge or canprovide an inert gas connection.

Copper bars 9 forming current feeders for the furnace heating elementare secured in diametrically opposed positions to the inside wall of thewater jacket by pins 10, passing through apertured bosses 11 in the wallof the jacket and threaded to receive nuts 12. The copper bars, whichare in the form of quadrants cut longitudinally from a hollow cylinder,fit closely against the water jacket in heat conducting relationshiptherewith. They are insulated from the jacket by thin strips 13 of micaor other electrically insulating material. The pins 10 are insulatedfrom the bosses 11 by means of insulating bushes 14, 15 between which isarranged an insulating ring 16 to form a gas or vacuum seal. Currentsupply connections are made to the ends of the pins protruding from thebosses.

The furnace heating element 17 which may be made of gnaphite, is in theform of a hollow cylinder slotted to provide a lengthy current path andprovided at its lower end with integral, axially extended arcuateportions which constitute supporting legs 18 which extendcircumferentially over diametrically opposed quadrants of thecircumference of the cylinder. The external diameter over the legs 18 isequal to the internal diameter between the inner surfaces of the copperbars 9, so that the bars may fit closely against the legs inelectrically conducting relationship therewith. The upper ends of thebars are provided with internal circumferential projections 19 and thelegs 18 are provided with complementary circumferential recesses 20 sothat the legs of the element can be inserted into the tubular waterjacket in the circumferential spaces between the bars, and the elementcan then be rotated to align the legs and bars, axial movement of theelement being prevented in this position by the projections engaging therecesses. This bayonet type joint allows for the ready fitting andremoval of the element.

Loosely mounted in the center of the plate 6 at the lower end of thejacket is a jack comprising a screwed spindle 21 on which is threaded alifting plate 22 provided with upstanding dowels 23. The spindle can berotated by means of a key inserted through the heating element from itsupper end to engage a square section portion on the upper end of thespindle.

The internal surfaces 24 of the lower ends of the supporting legs 18 ofthe heating element, are conical about the axis of the heating elementand a refractory or ceramic plug 25 of complementary frusto-conical formis arranged on the lifting plate 22 of the jack. Washers 26 withintereng aging spherical surfaces are arranged between the plate 22 andplug 25. The plug has recesses 27 which engage over the dowels 23, anaxial hole 28 to allow passage of the spindle 21 of the jack, and a counterbored axial hole 29 to receive the end of the key for operating thejack. The plug is in the form of a frustrum of a cone parts of which arecut away axially to leave diametrically opposed conical quadrantsalternating with diametrically opposed plane surfaces.

If the conical surfaces of the plug are aligned with the supporting legs18 of the heating element and the copper bars 9 the jack may be operatedto apply axial pressure to the legs 18, this pressure being transmittedthrough the conical sloping surfaces of the legs 18 in directionstransverse to the axis of the element, so that the legs 0 are clampedfirmly against the copper bars 9, and the bars are clamped firmlyagainst the wall of the water jacket.

specification 908,667, a pillar of refractory material is mounted in thecenter of the base plate and supports a cap of refractory material whichforms the furnace hearth and is surrounded by the heating element. Inthe furnace of FIGURE 1 this pillar of refractory material (60) isformed at its lower end so as to fit the counterbored hole 29 in theplug 25, the end of the pillar being recessed so as to clear theprojecting end of the spindle 21 of the jack.

The furnace is also provided with a water jacketed enclosure 30 in theform of an inverted pot remo vably mounted in a gas-tight manner on thebase plate to enclose the heating element. The element may be furthersurrounded by radiation shields 31 or by a second pot 32. In the lattercase the space between the pots is filled with lampblalck. A ring 33 isprovided to prevent upward movement of pot 32. These details aredescribed in specification 908,667.

In the modification shown in FIGURES 3 and 4, the interior surfaces ofthe copper bars 9 and the exterior surfaces of the supporting legs 18 ofthe heating element are of complementary conical form. A ring nut 34makes threaded engagement with the wall of the water jacket and isadapted to engage an insulating ring 35 arranged on shoulders 36provided on the supporting legs 18 to exert axial pressure thereon. Thesupporting legs 18 extend circumferentially over quadrants of a circleat their upper portions but their lower portions which contact thecopper bars 8 extend circumferentially to near semicircles. Thisdifference in cross-sections is shown clearly in FIGURE 4, in which viewthe Water jacket is omitted.

A distance piece 37 of refractory material is arranged diametrally inthe gap between the near semi-circular portions of the lower ends of thesupporting legs 18 so as to prevent inward radial movement of the legswhen the nut 34 is screwed down to apply axial pressure thereto. The topface of the distance piece is provided with a central axial recesscorresponding to the counterbored hole 29, FIGURE 1, so that a pillar ofrefractory material can be mounted therein for supporting a refractorycap forming a furnace hearth.

In both of the above described forms of the invention, axial pressure isapplied to a pair of mating conical surfaces to produce a wedging actionwhich causes the supporting legs of the heating element to pressradially outwardly into firm frictional and electrically conductingengagement with the current feeders; a uniform pressure is applied overthe whole of the contacting surfaces between the heating elementsupporting legs and the copper current feed bars, and between these feedbars and the wall of the water jacket.

The furnace is specially designed so that the heating element andcurrent feeders can be readily removed and replaced by an element andfeeders of different form.

The furnace base plate 3 is provided with additional apertures in whichare welded tubular bosses 38 which are of the same dimensions as thebosses 11 in the water jacket. These bosses are fitted with plugs 39provided with circumferential recesses containing gas sealing rings 40.Each plug is attached at one end by means of a circlip to an internallythreaded cap 41 adapted to be screwed on to the projecting end of one ofthe bosses which are suitably threaded externally.

When it is desired to use the alternative heating element, the heatingelements 17, the copper feed bars 9, and the jack are removed from thefurnace, and the gassealing plugs 39 are removed from the bosses 38 andfitted to the bosses 11 in the water jacket as shown in FIGURE of thedrawings. The alternative heating element shown in this figure comprisestungsten strips 42 arranged in parallel longitudinal spacedrelationship. At

the upper end of the element the ends of the strips are arranged betweenconcentric arcuate tantalum strips 43 to which they are rivetted. Theinner strip projects above the top of the element and is rivetted orbolted to tantalum arms or straps 44 secured at their outer ends tosplit brass blocks 45 adapted to be clamped to brass caps 46 fitted tothe upper ends of the current feeding tubes 47. At the lower end of theelement, the tungsten strips 42 are secured between a circular tantalumring 48 and arouate tantalum strips (not shown) rivetted together.

The current feeding tubes 47 are'mounted at their lower ends in tubularmetal sleeves 49 which also carry openended tubes 56 arrangedconcentrically within the tubes 47 and spaced therefrom. The sleeves 49are arranged in the tubular'bosses 38. Opposed insulating bushes 51abutting an insulating ring 52 adapted to form a gas seal are arrangedin the bosses 38 around the sleeves 49. A metal banjo fitting 53 isarranged on the sleeve to supply cooling water through holes 54 in theWall of the sleeve to the space between the tubes 47, 50. By means of anut 55 threaded on the sleeve the parts mounted thereon may be drawntogether to effect water-tightness and firm mounting of the sleeve inthe bosses 38. A plate 56 secured to the sleeve carries a button 57 ofceramic material adapted to engage a recess in the base plate 3 toprevent rotation of the sleeve.

When this alternative metal heating element is employed the radiationshields 31 are used to surround the element. Further, instead of thefurnace hearth being supported On a refractory pillar the base of theinverted pot 30 forming the furnace enclosure is adapted so that thefurnace charge can he introduced thereth-rough and suspended therefrom.

What is claimed is:

1. An electric furnace comprising a tubular resistance elementsubdivided to provide a path for the passage of heating current inexcess of the length of the element, said element having at one end aplurality of angularly spaced axially extended apertured arcuateportions constituting supporting legs for the element, a tubular waterjacket, a plurality of current feeders of arcuate cross section, eachlying longitudinally of the jacket between the jacket and one of saidleg portions closely adjacent thereto, insulatlon means interposedbet-ween an inner surface portron of the water jacket and the currentfeeders, whereby the current feeders are in heat-conducting relationshipwith said jacket hut electrically insulated therefrom, and IIIelectrically conducting relationship with the outer surface of said oneleg portion of the heating element, and releasable clamping meansoperable to press said leg portrons against the current feeders and thecurrent feeders against the jacket in a manner such that a substantiallyuniform pressure is exerted over the respective surfaces through whichheat transfer and the fiow of current occur.

2. An electric furnace in accordance with claim 1, wherein each of thesaid arcuate portions of the element is formed with a surface whichslopes relatives to the axis of the element, and the clamping means whenoperated applies axially directed pressure which is transmitted throughthe said sloping surfaces in directions transverse to the axis of theelement.

3. A furnace in accordance with claim 2, wherein each said arcuateportion has a conically tapering internal surface, and the clampingmeans comprises a plug having a complementary conical surface matingwith the said internal surfaces, the plug being axially movable,relative to the heating element to apply clamping pressure to the saidarcuate portions.

4. A furnace in accordance with claim 3,, wherein the clamping meanscomprises a screw jack for moving the plug axially of the heatingelement, the said screw jack being rotatable by means of a keyinsertable through the interior of the heating element.

5. A furnace in accordance with claim 3, wherein the plug is recessed toreceive the lower end of a refractory pillar carrying at its upper end arefractory cap forming the hearth of the furnace.

6. A furnace in accordance with claim 4, wherein a bayonet type joint isformed between the heating element and the current feeders, whereby theelement may be readily removed.

7. A furnace in accordance with claim 1, wherein the exterior surfacesof the said rarcuate portions of the heating element and the adjacentsurfaces of the current feeders are of complementary conically taperingform, the element being axially movable, relative to the current feedersby the said clamping means, and a spacing means is provided forpreventing the arcuate portions of the heating element from movingradially inwardly towards each other.

8. A furnace in accordance with claim 7 wherein the spacing means isrecessed to receive the lower end of a refractory pillar carrying at itsupper end a refractory cap forming the hearth of the furnace.

9. A furnace in accordance with claim 7, wherein the clamping meanscomprises a nut having threaded engagement with a fixed part of thefurnace and bearing against an abutment on the element.

10. A furnace in accordance with claim 1, wherein the current feedersare removably secured to the wall of the jacket by means of pins adaptedto be inserted into apertures in the Wall of the jacket and to beconnected to current supply leads externally of the jacket.

11. A furnace in accordance with claim 10 wherein the heating element isremovable, and also comprising a base plate including apertures forreceiving mounting means for an alternative form of heating element, andwith plugs for sealing the said apertures, said plugs beingalternatively insertable in the apertures in the wall of the jacket leftby the removal of the said pins.

12. A furnace in accordance with claim 1, and comprising a baseincluding :an aperture, and wherein the said water jacket is secured insaid aperture in the base and defines a duct through which the furnacecan be evacuated or an inert gas introduced.

13. An electric furnace comprising a base, an annular water jacket atthe base of the furnace, a plurality of current feeders shaped to fitclosely against the inner surface of the water jacket, a heating elementin the form of a hollow cylinder which is slotted to provide an extendedpath for the passage of heating current therealong, the element beingformed integrally with a plurality of axially extending angularly spacedterminal portions of armate cross section, each having a surface whichis conical about the axis of the element, the outer surface of each saidportion fitting closely against the inner surface of one of said currentfeeders, clamping means engageable with the element and adapted to applyaxially directed pressure thereto so as to create a wedging actionagainst said conical surfaces, said wedging action causing said arcuateportions to press radially outwardly int-o firm frictional andelectrically conducting engagement with said current feeders.

References Cited by the Examiner UNITED STATES PATENTS 2,859,425 11/1958Felton 339270 2,964,389 12/1960 Bennett et a1. 23-253 2,966,537 12/1960Witucki et a1. 13-22 2,971,039 2/1961 Western l325 3,012,090 12/1961Robbins 17452 3,129,314 4/1964 Hage et a1. 338- 238 X 3,160,693 12/1964Palmer 13-22 3,213,177 10/1965 Diefendor l331 FOREIGN PATENTS 406,567 3/1934 Great Britain.

RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Exa'miner.

V. Y. MAYEWSKY, Assista'nt Examiner.

1. AN ELECTRIC FURNACE COMPRISING A TUBULAR RESISTANCE ELEMENTSUBDIVIDED TO PROVIDE A PATH FOR THE PASSAGE OF HEATING CURRENT INEXCESS OF THE LENGTH OF THE ELEMENT, SAID ELEMENT HAVING AT ONE END APLURALITY OF ANGULARLY SPACED AXIALLY EXTENDED APERTURED ARCUATEPORTIONS CONSTITUTING SUPPORTING LEGS FOR THE ELEMENT, A TUBULAR WATERJACKET, A PLURALITY OF CURRENT FEEDERS OF ARCUATE CROSS SECTION, EACHLYING LONGITUDINALLY OF THE JACKET BETWEEN THE JACKET AND ONE OF SAIDLEG PORTIONS CLOSELY ADJACENT THERETO, INSULATION MEANS INTERPOSEDBETWEEN AN INNER SURFACE PORTION OF THE WATER JACKET AND THE CURRENTFEEDERS, WHEREBY THE CURRENT FEEDERS ARE IN HEAT-CONDUCTING RELATIONSHIPWITH SAID JACKET BUT ELECTRICALLY INSULATED THEREFROM, AND INELECTRICALLY CONDUCTING RELATIONSHIP WITH THE OUTER SURFACE OF SAID ONELEG PORTION OF THE HEATING ELEMENT, AND RELEASABLE CLAMPING MEANSOPERABLE TO PRESS SAID LEG PORTIONS AGAINST THE CURRENT FEEDERS AND THECURRENT FEEDERS AGAINST THE JACKET IN A MANNER SUCH THAT A SUBSTANTIALLYUNIFORM PRESSURE IS EXERTED OVER THE RESPECTIVE SURFACES THROUGH WHICHHEAT TRANSFER AND THE FLOW OF CURRENT OCCUR.